The present invention relates to a disk drive for use to write and/or read information on/from a disk storage medium (which will be herein simply referred to as a xe2x80x9cdiskxe2x80x9d), and more particularly relates to a disk drive that generates a minimized degree of vibration even when a disk is rotated at a high velocity.
In recent years, to increase the data transfer rates of various types of disk drives such as a CD-ROM drive, it has become more and more necessary to further increase the rotational velocity of the disk. However, the disk normally has unbalanced mass due to a variation in its thickness, for example, and has a center of mass at a position that has shifted from its real center (i.e., has an eccentric center of mass). When such a disk is rotated at a high velocity, an unbalanced centrifugal force (unbalanced force) is applied onto the center of rotation of the disk, thus generating some vibration in the disk drive. The magnitude of this unbalanced force increases proportionally to the square of the rotational frequency. Accordingly, as the rotational frequency of the disk is increased, the amplitude of the vibration increases steeply. That is to say, when the disk is rotated at a high velocity, the disk drive vibrates significantly, and cannot perform its write or read operation with good stability. Furthermore, the vibration generated is also transmitted to external units outside of the disk drive. Thus, when such a disk drive is built in a computer, for example, other peripheral units are affected as well by the vibration that has been transmitted thereto. In view of these considerations, to increase the data transfer rate by increasing the rotational velocity of the disk, the vibration of the disk drive needs to be minimized.
To overcome the problems described above, according to a known technique, the vibration of a disk drive is minimized by getting the mass eccentricity of a disk corrected automatically by an auto-balancer, which includes balancing members such as balls. This technique is disclosed in Japanese Patent Publication No. 2824250, for example. Hereinafter, the configuration and operation of a conventional disk drive including the auto-balancer will be described with reference to FIGS. 18 and 19.
FIG. 18 is a cross-sectional view illustrating a configuration for the conventional disk drive. This disk drive includes a spindle motor 2 with a turntable 18, and an auto-balancer 16. A disk 1 is sandwiched between the turntable 18 and the auto-balancer 16. By driving the spindle motor 2, the disk 1 rotates along with the turntable 18 around a rotation axis P0.
As shown in FIG. 19, the auto-balancer 16 includes a hollow ring portion 23 that is concentric with the rotation axis P0. Inside the hollow ring portion 23, multiple balancing members 17 are stored. The balancing members 17 may be a number of iron balls, for example, and can move inside the hollow ring portion 23.
Referring back to FIG. 18, the spindle motor 2 is secured to a sub-base 6, which in turn is fixed to a main base 8 by way of insulators (first elastic members) 7 that serve as elastic members. The vibration and impact that are externally applied to the sub-base 6 by way of the main base 8 are dammed by the insulators 7.
The vibration system that is made up of the main base 8, sub-base 6 and insulators 7 has a natural frequency (i.e., resonance frequency) at which vibration is transmitted from the main base 8 to the sub-base 6 at the maximum transmissibility. In this disk drive, the natural frequency f1 in a mode in which the sub-base 6 vibrates parallelly to the recording surface of the disk 1 is defined to be lower than the rotational frequency fm of the disk 1 by selecting an appropriate material for the insulators 7 or by any other suitable technique. For example, when the rotational frequency fm is 100 Hz, the natural frequency f1 may be set to 60 Hz.
Hereinafter, it will be described how the conventional disk drive having such a configuration operates to rotate a disk having an eccentric center of mass. As shown in FIG. 19, the center of mass G1 of the disk 1 is located at a position that has shifted from the rotation axis P0. Accordingly, when the disk 1 is rotated, a centrifugal force F is generated and oriented from the rotation axis P0 toward the center of mass G1. The specific direction in which this centrifugal force F is applied changes as the disk rotates. It should be noted that this centrifugal force F is generated due to the unbalanced mass of the disk 1 and will be herein sometimes referred to as an xe2x80x9cunbalanced forcexe2x80x9d. When such an unbalanced force F is applied, the disk 1 and the sub-base 6 make a whirling motion with respect to the main base 8.
In this case, the whirling motion changes in accordance with the relationship between the rotational frequency fm of the disk 1 and the natural frequency f1. Specifically, if the rotational frequency fm of the disk 1 is sufficiently lower than the natural frequency f1, then no phase delay is created and the direction in which the unbalanced force F is applied (from the rotation axis P0 toward the center of mass G1) is the same as the direction in which the sub-base 6 is displaced (see FIG. 20(a)). On the other hand, if the rotational frequency fm is sufficiently higher than the natural frequency f1 as described above, then a phase delay is created. Accordingly, the direction in which the unbalanced force F is applied becomes substantially opposite to the direction in which the sub-base 6 is displaced (see FIG. 20(b)). In this case, the whirling center axis P1 is located between the center of mass G1 of the disk and the rotation axis P0.
Hereinafter, it will be described how the auto-balancer 16 operates when the whirling center axis P1 is located between the center of mass G1 of the disk and the rotation axis P0. While the whirling motion is being made, a centrifugal force q is applied from the whirling center axis P1 toward the balancing members 17 that are stored inside the hollow ring portion 23. On the other hand, a drag force N is also applied from the outer sidewall 25 of the hollow ring portion 23 toward the balancing members 17. This drag force N is applied toward the rotation axis (i.e., the center of rotation) P0 that is also the center of the auto-balancer 16 and the center of the outer sidewall 25. Consequently, a moving force R is applied as a resultant force of the centrifugal force q and the drag force N to the balancing members 17 in a tangential direction of the hollow ring portion 23. This moving force R moves the balancing members 17 along the outer sidewall 25. As a result, the balancing members 17 gather toward a position that is substantially opposite to the center of mass G1 of the disk 1 with the whirling center axis P1 interposed between them. That is to say, while the disk 1 is being rotated, the auto-balancer 16 operates in such a manner as to have its center of mass located on an extension of the line that connects together the center of mass G1 of the disk 1 and the whirling center axis P1. Thus, a centrifugal force Q is applied to the auto-balancer 16 in the direction opposite to the direction in which the unbalanced force F is applied. That is to say, the unbalanced force F is canceled by this centrifugal force Q, thus decreasing the magnitude of the force being applied to the sub-base 6. Consequently, the vibration of the sub-base 6 can be reduced.
In this disk drive, however, if the unbalanced force F being canceled decreases, then the moving force R applied to the balancing members 17 also decreases. In such a situation, the balancing members sometimes cannot reach their ideal positions because the balancing members receive a frictional resistance from the hollow ring portion 23, for example. Then, the desired vibration damping effects are not achievable and a residual vibration is generated. Also, the residual vibration may have not only a component that is parallel to the disk plane but also a component that is vertical to the disk plane as well. In that case, various problems arise. For example, a so-called xe2x80x9ccrosstalkxe2x80x9d phenomenon is created to increase the vertical vibration unintentionally.
In addition, in the conventional disk drive described above, it is difficult to provide the auto-balancer and the disk plane on the same plane. Accordingly, the level difference between the centrifugal force applied to the auto-balancer and that applied to the eccentric center of mass of the disk generates a moment, thus increasing the vibration in a direction in which the rotation axis of the disk tilts. When the vibration increases in that direction in which the rotation axis of the disk tilts, the smooth movement of the balancing members may sometimes be interfered with. As a result, the ability of the auto-balancer to correct the mass eccentricity of the disk declines.
If the disk is rotated at a higher velocity, the centrifugal force applied to the center of mass increases proportionally to the square of the number of revolutions. Accordingly, even if the distance between the center of mass of the disk that has been corrected by the auto-balancer and the center of rotation is relatively short, a relatively great vibration is generated. For that reason, it is difficult for the conventional disk drive including the auto-balancer to increase the data transfer rate by rotating the disk at a higher velocity.
On the other hand, according to another known technique, the vibration of a disk drive may also be reduced by getting the vibration, which is generated by rotating a disk with an eccentric center of mass, absorbed into a dynamic vibration absorber. Such a technique is disclosed in Japanese Laid-Open Publication No. 11-328944 and Japanese Patent Publication No. 2951943, for example. In this technique, a dynamic vibration absorber having predetermined mass is connected to a member (e.g., the sub-plate 6), which vibrates (or whirls) with the rotation of a disk having an eccentric center of mass, by way of an elastic member. The dynamic vibration absorber functions in such a manner as to absorb the vibration generated.
In the method of reducing the vibration of the disk drive by using the dynamic vibration absorber, however, the centrifugal force itself, which is generated when the disk having an eccentric center of mass is rotated, cannot be reduced. Accordingly, the spindle motor or the base should have rigidity that is great enough to overcome the centrifugal force applied to the eccentric center of mass. Furthermore, to minimize the vibration effectively, the mass of the disk drive and the dynamic vibration absorber should be increased proportionally to the square of the number of revolutions of the disk. Accordingly, the disk drive should increase its own weight excessively, which is a problem.
In order to overcome the problems described above, an object of the present invention is to provide a disk drive that can minimize the vibration to be generated when a disk having an eccentric center of mass is rotated at a high velocity and thereby can perform a write or read operation with good stability.
A disk drive according to the present invention includes: a motor with a rotating portion to rotate a disk thereon; an auto-balancer, which is connected to the rotating portion of the motor and which is able to change its center of mass; a base, which is secured to the motor and which is connected to an external member by way of a first elastic member; and a dynamic vibration absorber, which is connected to the base by way of a second elastic member. In this disk drive, if the disk makes a whirling motion while being rotated by the motor, a relationship between a first natural frequency of a first vibration system, which includes the base, the first elastic member and the external member, as measured parallelly to a base plane and a rotational frequency of the disk and a relationship between a second natural frequency of a second vibration system, which includes the dynamic vibration absorber, the second elastic member and the base, as measured parallelly to the base plane and the rotational frequency of the disk are defined so that a phase angle of 120 degrees to 180 degrees is formed between a direction that is pointed from a whirling center axis toward a center of mass of the disk and a direction that is pointed from the whirling center axis toward the center of mass of the auto-balancer.
In a preferred embodiment, the disk drive rotates the disk at a frequency that is substantially equal to a third natural frequency of the second vibration system as measured vertically to the base plane.
In another preferred embodiment, the first natural frequency is at most 1/√{square root over (2)} time as high as the rotational frequency of the disk.
In another preferred embodiment, the second natural frequency is 1.05 to 2 times as high as the rotational frequency of the disk.
In another preferred embodiment, the auto-balancer includes a hollow ring member and moving members that are stored inside the hollow ring member so as to be movable therein.
In another preferred embodiment, the auto-balancer is secured to the rotating portion of the motor.
In another preferred embodiment, vibration is transmitted from the external member to the base at a transmissibility of greater than three at the first natural frequency.
In another preferred embodiment, vibration is transmitted from the base to the dynamic vibration absorber at a transmissibility of greater than three at the second natural frequency.
In another preferred embodiment, the first elastic member is made of either a silicone rubber material or a natural rubber material.
In another preferred embodiment, the second elastic member is made of either a silicone rubber material or a natural rubber material.
In another preferred embodiment, the auto-balancer is provided on both sides of the disk.
In another preferred embodiment, the center of mass of the dynamic vibration absorber is located within a plane that is parallel to the disk plane and that is leveled with the center of thickness of the disk.
In another preferred embodiment, the center of mass of the dynamic vibration absorber is located on an axial line that defines the rotation center axis of the disk.
In another preferred embodiment, the dynamic vibration absorber is provided between the disk and the base.
Another disk drive according to the present invention includes: a motor with a rotating portion to rotate a disk thereon; an auto-balancer, which is connected to the rotating portion of the motor and which is able to change its center of mass; a base, which is secured to the motor; and a dynamic vibration absorber, which is connected to the base by way of multiple elastic members. A natural frequency of the dynamic vibration absorber in a translational mode in which the absorber makes a translational motion with respect to a base plane of the base is different from a natural frequency of the dynamic vibration absorber in an angular displacement mode in which the absorber is displaced angularly with respect to the base plane of the base.
In a preferred embodiment, the natural frequency in the translational mode is higher than a rotational frequency of the disk, and the natural frequency in the angular displacement mode is substantially equal to the rotational frequency of the disk.
In another preferred embodiment, the natural frequency in the angular displacement mode is defined by adjusting a distance between a center of mass of the dynamic vibration absorber and the multiple elastic members that support the dynamic vibration absorber thereon.
In another preferred embodiment, the natural frequency in the angular displacement mode is defined by adjusting a moment of inertia around the center of mass of the dynamic vibration absorber.
In another preferred embodiment, each of the multiple elastic members is provided between the inner wall of an opening of the base and a convex fixing member. The fixing member is connected to the dynamic vibration absorber and inserted into the opening.
In another preferred embodiment, the convex fixing member extends through the dynamic vibration absorber, and the top of the fixing member that extends through the dynamic vibration absorber is fixed to the dynamic vibration absorber at one end thereof by a press-fixing technique in which the top is heated and crushed.
In another preferred embodiment, the fixing member includes a rotation stopping portion, and the dynamic vibration absorber is screwed to the fixing member.
Still another disk drive according to the present invention includes: a motor with a rotating portion to rotate a disk thereon; an auto-balancer, which is connected to the rotating portion of the motor and which is able to change its center of mass; a base, which is secured to the motor; and a dynamic vibration absorber, which is connected to the base by way of an elastic member. In the disk drive, a natural frequency of the dynamic vibration absorber in a mode in which the absorber makes a translational motion with respect to a base plane of the base is different from a natural frequency of the dynamic vibration absorber in a mode in which the absorber makes a translational motion vertically to the base plane of the base.
In a preferred embodiment, the natural frequency in the mode in which the absorber makes the translational motion with respect to the base plane is higher than a rotational frequency of the disk, and the natural frequency in the mode in which the absorber makes the translational motion vertically to the base plane of the base is substantially equal to the rotational frequency of the disk.